An electromagnetic brake may be used for braking of a hoisting machine of an elevator, for braking of an elevator car or for braking of an escalator or a conveyor, for example.
The electromagnetic brake usually includes a stationary brake body and an armature arranged to move relative to the brake body. A spring or corresponding is fitted between the brake body and the armature to apply a thrust force between them. Additionally, an electromagnet with a magnetizing coil is fitted inside the brake body. Brake is disposed in the proximity of an object to be braked, such as a traction sheave of a hoisting machine or a guide rail of an elevator. The brake is applied by driving the armature against the object by means of the thrust force of the spring. Brake is opened by energizing the magnetizing coil. When energized, magnetizing coil causes attraction between the brake body and the armature, which further causes armature to disengage the braked object by resisting thrust force of the spring.
The magnetizing coil is energized/brake is opened by feeding current to the magnetizing coil. A brake controller may be used to selectively open or close the brake according to commands from elevator control. For this reason the brake controller has a main circuit for selectively feeding current to the magnetizing coil or cutting off the current of the magnetizing coil. In normal operation, brake is opened when starting a new elevator run and brake is applied at the end of the run.
To improve brake operation, e.g. to reduce brake noise, reduce heating of the magnetizing coil, adjust brake operation time etc., brake controller may have an adjustable output. For example, it has been suggested to use a controllable solid state switch, such as igbt transistor, mosfet transistor or silicon carbide (SiC) mosfet transistor in the brake controller main circuit to adjust current of the magnetizing coil. However, a further need exists to improve at least reliability and life time of such brake controllers.